The present invention relates to a magnetic recording apparatus and a magnetic recording medium for magnetically recording and reproducing information and a manufacturing method thereof.
A magnetic recording medium in a form of a rigid magnetic disk apparatus is widely used for a personal data file, a communication server, a large-scale computer file and the like. Also, a magnetic recording medium in a form of a magnetic tape apparatus is widely used for image or audio files for personal use or broadcasting. This is because a magnetic recording medium constituted by an ensemble of magnetic crystal grains shows a very high magnetization reversal rate, and therefore, a very high recording data transfer rate in an order of several hundreds Mbps or more, and also can attain a high recording density of about several tens Gb/in2. As for the magnetic recording medium, a higher transfer rate and a higher recording density are expected in a situation toward forthcoming multimedia era that amount of information continues to increase remarkably.
An areal recording density of the magnetic recording medium, particularly of a hard disk drive (HDD), has been improved by 60% or more per year over the past five years or more, and currently reaches several Gb/in2. Such improvement in areal density is owing to innovation and improvement of various elemental technologies such as use of a magnetoresistive reproducing system, use of a recording magnetic pole material having a high saturation magnetic flux density, improvement in processing of magnetic head of a narrow track width, use of a magnetic head having a narrower gap, miniaturization and high-precision processing of a slider, high-precision servo technology, and development of novel modulation/demodulation technology represented by PRML. In addition, with respect to a magnetic recording medium itself, there is advanced progress in elemental technologies such as smoothing and flattening of medium surface leading to low flying height operation of a magnetic head, reduction in magnetization transition width due to increase in coercivity and decrease in thickness of a magnetic layer, and medium noise reduction due to decrease in exchange interaction between magnetic grains and reduction in magnetic grain size.
In the aforementioned conventional so-called multigrain magnetic recording medium, it is supposed that, if isolation of magnetic grains and reduction in magnetic grain size are advanced to ensure low noise, the recording density will be limited because of thermal disturbance. Hereinafter, the thermal disturbance will be described.
For improvement of a recording density, it is necessary to reduce a recording cell size on a medium, which brings about reduction in signal magnetic field intensity generated from the medium. In order to meet an S/N ratio required for a recording system, noise must be reduced corresponding to reduction in signal intensity. The medium noise is mainly caused by fluctuation of a magnetization transition, and the fluctuation is proportional to a size of a magnetization reversal unit made of magnetic grains. Therefore, in order to reduce the medium noise, it is required to isolate magnetic grains by disrupting exchange interaction between magnetic grains, i.e., to reduce the fluctuation of the magnetization transition to an order of a size of single magnetic grain, and to reduce magnetic grain size.
Magnetic energy that a single isolated magnetic grain has is given by a product of magnetic anisotropy energy density and volume of the grain. To reduce a medium thickness in order to reduce a magnetization transition width and to reduce a magnetic grain size in order to meet a requirement for low noise significantly lowers the volume of magnetic grain, and further significantly lowers magnetic energy of the grain. If the magnetic energy of a certain grain is several hundred times of thermal energy at an operating temperature (at least at room temperature) for a magnetic memory, resistance against thermal disturbance is considered to be sufficient. However, if the magnetic energy of the grain is less than a hundred times of thermal energy, there is possibility that the magnetization direction of the magnetic grain is reversed by thermal disturbance and recorded information is lost. Because of the thermal disturbance, it is thought that the areal density of HDD will be limited to about 40 to 50 Gb/in2.
A conventional multigrain magnetic medium such as CoCr-based medium has a structure in which a Cr-rich non-magnetic grain boundary is segregated between magnetic grains in order to lower exchange coupling between magnetic grains. However, in a method of fabricating a magnetic film by conventional sputtering, diameters of magnetic grains cannot be adjusted directly, and it is difficult to reduce the magnetic grain size uniformly. Thus, there is large distribution in grain diameter and intergranular distance, and grains are arranged irregularly. Therefore, even if exchange interaction between grains is severed to isolate grains, medium noise is not sufficiently lowered, which inhibits improvement in recording density. Specifically, when distribution in grain diameter is expressed by full width at half maximum (FWHM) of distribution of grain diameters, a value of about xc2x150% is exhibited in a typical medium, and a value of xc2x125% or more is exhibited even in a medium in which distribution is controlled by low-speed sputtering or the like. For example, a typical medium of 20 nm in average grain diameter has a number of grains between 10 nm and 30 nm. This means that there are considerable grains of less than 10 nm in grain diameter, which are strongly affected by thermal disturbance. Distribution in intergranular distance is more significant: the distribution is xc2x170% in FWHM in a typical medium, and is xc2x145% or more even in a well controlled medium. That is, a typical medium of 2 nm in intergranular distance has a number of grains of 0.6 nm to 3.4 nm in intergranular distance. This means that there are considerable grains in an exchange coupled state.
There has been proposed some solutions to overcome the problem of thermal disturbance. One solution is use of a magnetic material with high magnetic anisotropy. However, if the magnetic anisotropy becomes higher, the recording saturation magnetic field required for a medium is increased, and it is required to further increase saturation magnetic flux density of a magnetic pole material for recording head. This cannot be a practical solution because currently available soft magnetic film material, including laboratory level, is hard to meet the above requirements.
Another solution is light thermal assisted recording. In this method, a highly anisotropic magnetic material is employed, and a recording portion is heated by light irradiation during recording. This lowers the anisotropy of magnetic grains and the recording saturation magnetic field, and therefore, recording can be performed with an available recording head. However, this method is impractical because it requires providing an optical system in a drive unit having almost no extra space, including a space between disks. In addition, this method increases power-consumption, and brings about additional heat generation.
As another technical seed to avoid the problem of thermal disturbance for overcoming the HDD recording density limit, there has been proposed a near field optical recording employing SIL or evanescent light. However, optical recording cannot achieve high transfer rate like magnetic recording as long as a heat mode process is employed. On the other hand, there has been proposed a method employing a photon mode material in order to attain a ultrahigh transfer rate and ultrahigh density, but such a method is in a research level and not realized at all.
The foregoing methods cannot give a proper solution to thermal disturbance that prevents higher recording density of magnetic media.
Currently, it is considered that effective methods to solve thermal disturbance are use of a magnetic recording medium in which magnetic particles are arrayed regularly in a non-magnetic matrix (hereinafter, referred to as an ordered magnetic particle medium) and use of a magnetic recording medium in which non-magnetic particles (pores) are arrayed regularly in a continuous magnetic material (hereinafter, referred to as an ordered non-magnetic pore medium).
First, an ordered magnetic particle medium will be described. A magnetic recording medium comprising regularly arrayed magnetic particles is described, for example, in J. Appl. Phys. 76 (10) 6673, 1994. This medium is manufactured by coating an Au seed layer and a resist on an Si wafer, exposing the resist by electron beam (EB) direct write, developing the resist to form pores, and depositing Ni in the pores by plating, thereby forming a regularly arrayed Ni pillar array of 35 nm in diameter with distance of 100 nm. The medium studied in the above paper is directed to magnetic recording application, but there is no particular disclosure on how to use it. In this paper, there is merely suggested that the medium has a pattern with distance of 100 nm, thus making it possible to ensure the recording density of 65 Gb/in2. In this paper, it is assumed that a single magnetic particle is regarded as a minimum recording unit, and there exists a single magnetic particle in a minimum recording cell. However, there is no description on devices such as magnetic head and servo system for performing recording and reproducing using such a small recording unit.
Examples of media comprising regularly arrayed magnetic particles fabricated by using EB direct write are also disclosed in J. Vac. Sci. Technol. B13 (6) 2850, 1995 and J. Vac. Sci. Technol. B12 (6) 3196, 1994. In these papers, although processes for fabricating regularly arrayed magnetic particles other than EB direct write are slightly different from each other, the concept that a single magnetic particle is assumed to be a minimum recording unit is common. In addition, in these papers, there is no description on distribution of magnetic particle diameter and distribution of inter-particle distance.
However, the EB direct write method cannot be used for industrial manufacturing of magnetic media from the viewpoints of cost and productivity, although the method can be employed to fabricate samples at laboratory level. In addition, in the case where a single magnetic particle is used as a minimum recording unit, significant burdens are imposed to improve elemental technologies other than the medium: for example, remarkable reduction in a track width of the recording/reproducing head, remarkable improvement in sensitivity of the reproducing head, remarkable improvement in servo precision or the like. Further, when a single particle constitutes one recording cell, the medium noise is high, and therefore, sufficient S/N ratio cannot be obtained, even if a head with high resolution is used.
Conventionally, an address pattern or a servo pattern in a magnetic medium is formed by a magnetic disk drive manufacturer by magnetically recording the patterns (so-called servo write). A method of forming the address pattern or the servo pattern by thin-film patterning is proposed in J. Appl. Phys. 69 (8) 4724, 1991. However, the medium employed in this paper does not have regularly arrayed magnetic particles.
In Jpn. J. Appl. Phys. 30 (2) 282, 1991 and J. Electrochem. Soc. 122 (1) 32, 1975, methods of manufacturing a magnetic medium by depositing a magnetic material in porous alumite by plating are disclosed. In these methods, however, a matrix is limited to Al2O3, and a magnetic material is limited to Co, Coxe2x80x94Cr, Coxe2x80x94Ni, Fexe2x80x94Cu, Fexe2x80x94P or the like to which plating is applicable.
Next, an ordered non-magnetic pore medium will be described. For example, a medium in which non-magnetic pores are arrayed in a magnetic continuous film, which is referred to as a network medium, is disclosed in IEEE-Trans. Magn. 34 (4), 1609, 1998. This paper relates to noise simulation of an imaginary medium in which non-magnetic pores are arrayed regularly in a multigrain magnetic film. In this paper, there is no description on non-magnetic pore diameter, distribution of inter-pore distance, address pattern, and servo pattern.
An object of the present invention is to provide a magnetic recording apparatus and a magnetic recording medium capable of improving S/N ratio and achieving high density and a manufacturing method thereof.
According to one aspect of the present invention, there is provided a magnetic recording apparatus comprising a magnetic recording medium comprising a magnetic recording layer formed on a substrate, a recording head configured to record information by forming recording cells on recording tracks formed on a surface of the magnetic recording layer, and a reproducing head configured to reproduce information recorded in the recording cells, wherein the magnetic recording layer has a structure that magnetic particles are dispersed in a non-magnetic matrix and ordered particle domains in which magnetic particles are arrayed regularly are formed on a surface thereof, and wherein the size in the track width direction of each ordered particle domain is one fifth or more of a track width of the reproducing head.
According to another aspect of the present invention, there is provided a magnetic recording apparatus comprising a magnetic recording medium comprising a magnetic recording layer formed on a substrate, a recording head configured to record information by forming recording cells on recording tracks formed on a surface of the magnetic recording layer, and a reproducing head configured to reproduce information recorded in the recording cells, wherein the magnetic recording layer has a structure that non-magnetic particles are dispersed in a magnetic matrix and ordered particle domains in which non-magnetic particles are arrayed regularly are formed on a surface thereof, and wherein the size in the track width direction of each ordered particle domain is one fifth or more of a track width of the reproducing head.
A magnetic recording medium according to the present invention comprises a magnetic recording layer formed on a substrate, in which information is recorded by forming recording cells in recording tracks formed on a surface of the magnetic recording layer, wherein the magnetic recording layer has a structure that magnetic particles are dispersed in a non-magnetic matrix and ordered particle domains in which magnetic particles are arrayed regularly are formed on a surface thereof, and wherein the size in the track width direction of each ordered particle domain is one fifth or more of a width of the recording track formed on the recording layer.
Another magnetic recording medium according to the present invention comprises a magnetic recording layer formed on a substrate, in which information is recorded by forming recording cells in recording tracks formed on a surface of the magnetic recording layer, wherein the magnetic recording layer has a structure that non-magnetic particles are dispersed in a magnetic matrix and ordered particle domains in which non-magnetic particles are arrayed regularly are formed on a surface thereof, and wherein the magnetic matrix is constituted by magnetic crystal grains separated from each other with an average distance of 2 nm or less, and wherein an average non-magnetic particle diameter is 1 nm or more.
Another magnetic recording medium according to the present invention comprises a magnetic recording layer formed on a substrate, in which information is recorded by forming recording cells in recording tracks formed on a surface of the magnetic recording layer, wherein the magnetic recording layer has a structure that magnetic particles are dispersed in a non-magnetic matrix, the magnetic particles being arrayed regularly on a surface thereof, and wherein the number of the magnetic particles arrayed along the track length direction in the minimum recording cell is four or more, and wherein the full width at half maximum of distribution of the distance between closest magnetic particles is xc2x140% or less to an average distance between closest magnetic particles, and wherein the full width at half maximum of distribution of magnetic particle diameter is xc2x120% or less to an average magnetic particle diameter.
Still another magnetic recording medium according to the present invention comprises a magnetic recording layer formed on a substrate, in which information is recorded by forming recording cells in recording tracks formed on a surface of the magnetic recording layer, wherein the magnetic recording layer has a structure that non-magnetic pores are dispersed in a continuous magnetic film, the non-magnetic pores being arrayed regularly on a surface thereof, and wherein magnetization transitions in the continuous magnetic film are made by domain walls connecting the non-magnetic pores, and wherein an average non-magnetic pore diameter ranges from 0.5 to 3 times of an average domain wall width.
A method of manufacturing a magnetic recording medium according to the present invention comprises steps of forming a block copolymer layer on a non-magnetic layer, making the block copolymer layer to form a sea-island structure by self-organized manner in which the ratio of the etching speed between sea and island is three or more, etching the non-magnetic substrate through the block copolymer layer having the sea-island structure, depositing a magnetic layer in an etched region of the non-magnetic substrate, and lifting-off remaining polymer layer and the magnetic layer on the polymer layer.
Another method of manufacturing a magnetic recording medium according to the present invention comprises steps of forming an underlayer on a substrate, forming a non-magnetic layer on the underlayer, forming a block copolymer layer on the non-magnetic layer, making the block copolymer layer to form a sea-island structure by self-organized manner in which the ratio of the etching speed between sea and island is three or more, etching the non-magnetic layer through the block copolymer layer having the sea-island structure, depositing a magnetic layer in an etched region of the non-magnetic layer, and lifting-off remaining polymer layer and the magnetic layer on the polymer layer.
Another method of manufacturing a magnetic recording medium according to the present invention comprises steps of forming a magnetic layer on a substrate, forming a block copolymer layer on the magnetic layer, making the block copolymer layer to form a sea-island structure by self-organized manner in which the ratio of the etching speed between sea and island is three or more, etching the magnetic layer through the block copolymer layer having the sea-island structure, depositing a non-magnetic layer in an etched region of the magnetic layer, and lifting-off remaining polymer layer and the non-magnetic layer on the polymer layer.
Another method of manufacturing a magnetic recording medium according to the present invention comprises steps of forming a continuous non-magnetic film on a substrate, putting a self-organized mask having regularly arrayed holes on the continuous non-magnetic film, etching the continuous non-magnetic film through the mask, thereby forming regularly arrayed holes in the continuous non-magnetic film, and depositing a magnetic material in the holes formed in the continuous non-magnetic film, thereby forming magnetic particles.
Another method of manufacturing a magnetic recording medium according to the present invention comprises steps of, forming a continuous magnetic film on a substrate, forming a resist layer on the continuous magnetic film, putting a self-organized mask having regularly arrayed holes on the continuous magnetic film, exposing the resist layer through the mask and developing the resist layer, thereby forming a resist pattern having remaining regions corresponding to the holes, etching the continuous magnetic film through the resist pattern, thereby forming magnetic particles, and depositing a non-magnetic film in a region between the magnetic particles.
Still another method of manufacturing a magnetic recording medium according to the present invention comprises steps of forming a continuous magnetic film on a substrate, putting a self-organized mask having regularly arrayed holes on the continuous magnetic film, etching the continuous magnetic film through the mask, thereby forming regularly arrayed holes in the continuous magnetic film, and depositing a non-magnetic material in the holes formed in the continuous magnetic film, thereby forming non-magnetic pores.